Roller Compacted Concrete (RCC) is concrete, but it is placed by non-traditional methods which require a drier or stiffer consistency. RCC can have a much broader range of material properties than conventionally placed concrete, for example, it can use aggregates not meeting normal requirements, it can be placed at very high production rates, and it can be much less expensive.
By definition, RCC is concrete comprising a mixture of cement, sand, aggregate, such as gravel, stone, sand and the like, and water, having a consistency allowing it to be compacted with a heavy vibratory roller, for example, a ten-ton roller intended for asphalt and granular base. RCC is usually mixed in a continuous process, rather than in batches, delivered with trucks or conveyors, spread in layers using a bulldozer, and given final compaction with a vibratory roller.
RCC has generally been used for applications such as dam construction, pavement and bridge deck construction requiring a thick topping, usually two inches, as an essential element to achieve the required strength and fatigue life of the exterior slabs.
Conventional poured mass concrete is designed to have the highest fluidity by use of water and additives, the RCC formulation has the same ingredients as conventional concrete, i.e., cement, water, and aggregates, but unlike conventional concrete it is a drier mix stiff enough to be compacted by vibratory rollers. The pressure applied during the compaction phase of the mix implies a need of the highest possible initial density to ensure superior compressive strength, this can be reached by reducing the water level, however if the level is below the hydration level, the cured concrete will not reach the optimum properties. Therefore, current RCC mixes still have a water content that is at best a compromise between the full cure and the lowest slump of the concrete during the application of the vibratory rollers. There is a need in the industry for an RCC formulation that has the right amount of water to achieve a correct amount of hydration and also has the highest initial compressive strength.
Surfactants decrease the need for excess water, while making the concrete mix pourable, as if excess water was present. When surfactants are introduced into the concrete, the result is a less porous and somewhat stronger product. The strength increase is attributed to lower water/cement ratio and decrease in porosity. While surfactants improve the resistance to water penetration, surfactants alone provide too little improvement to be considered a solution to the problem.
Attempts have been made to increase the early strength of cement aggregate products, particularly concrete blocks, concrete masonry units, and the like, by adding an accelerator, such as calcium chloride triethanolamine or sodium silicate, to the mix or subjecting the product to steam or using type III cement. However, the addition of these accelerators, or the use of steam, increases the cost of producing the product and often its production time.
Another attempt provides for compositions, and a process for improving the early strength of cement aggregate products, in a stabilized aqueous emulsion with a surfactant such as alkali metal salts of fatty acids, alkali metal salts of sulfated fatty acids, alkali metal alkyl sulfates, alkali metal alkyl sufonates, alkali metal aryl sufonates, alkali metal alkyl lauryl sulfonate, alkali metal salts of alkylated naphthalene, alkali metal salts of lignosulfonic acid, condensation products of ethylene oxide and polyalkylene glycols, fatty acid glycerides, fatty acid amides, polyethylene sorbitol esters of fatty acids, quaternary ammonium halides, sorbitan esters, sulfonated or sulfated fatty acid esters or amides, and sulfonic acid. Results were achieved with sodium lignosulfonate as the surfactant, particularly with slack wax as the waxy substance in the emulsion.
The prior art indicates that the introduction of a wax in a solvent into the composition of water, cement, and aggregate used to produce a concrete product caused the resulting concrete to have substantially less strength than the concrete product produced from a substantially identical composition without the wax. It is believed that the wax coated the aggregate particles and inhibited the adherence of the cement paste to the aggregate causing the weakening as measured by testing the compressive strength. Therefore, the use of waxes in cement formulations for RCC application was not previously advisable.